The cast of 'Call The Midwife' have admitted they struggle to hide their emotions thanks to the heart-warming script of the hit BBC show.

The inhabitants of Nonnatus House, whose task is to bring babies into the world, are back for a nativity-themed festive special on Christmas Day.

And the latest emotional storylines involve an under-age pregnancy and a broken old lady in need of care.

Miranda Hart plays Chummy, who helps deal with one particularly emotionally-charged situation involving an under-age pregnancy and the effect it has on the young girl and her family.

"She helps a young girl who fell pregnant deal with the shame of telling her parents and potentially having to give the child up for adoption," explained Miranda. "It was very moving. And the actress who played the part was so young but so mature and a brilliant actress already."

Co-star Jenny Agutter revealed that she found it very hard to be as calm as her character Sister Julienne during the birth scenes, one of which opens the Christmas special.

The actress says: "I found myself very emotionally involved with that birth scene. I found the moment of holding this baby overwhelmingly emotional but that's not Sister Julienne so it was very important to sit on that."

Even the few men in the cast struggle to hold back the tears sometimes. Ben Caplan, who plays Chummy's husband PC Peter Noakes, has just welcomed a baby himself, so found himself welling up when the birth scenes were being filmed. "It does get you, you can't help it, whether you're acting in it or watching it," he said.

"There's something about the show which just gets hold of you and you can't resist it. You are overwhelmed by the stories and you care about the people."